you may try to save image into local file and set the url of file instead of image name in web view.
try the following
NSData* data = UIImagePNGRepresentation(yourDynamicImage);
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentDirectory = [paths objectAtIndex:0];
NSString* file= [documentDirectory stringByAppendingPathComponent:@"image.png"];
[data writeToURL:[NSURL URLWithString:file] atomically:YES];
NSURL url = [NSURL fileURLWithPath:file];
// pass the [url absoluteString] to the web view this should work